Seal for floating roof tanks



Feb. 2l, 1950 J. w. ALLEN 2,497,850

- SEAL FOR FLOATING RooF TANKS Filed Aug. e, 1945 2 sheets-sheet 1 ff O22g. E, A? /0 fi/Q5 nnllgllillnn nnnnnn I Feb. 21, 1950 J. w. ALLEN2,497,850

SEAL FOR FLOATING ROOF' TANKS Filed Aug.l 6, 1945 2 Sheets-Sheet 2ritmica Feb. 21, 195o SEAL Foa noA'rrNG RooF rANxs John W. Allen,Chicago, Ill., assigner to Chicago Bridge Iron Company ApplicationAugust 6, 1945, Serial No. 609,049

(Cl. 22o-85) BClaims.

This invention relates to a storage tank for liquids of the type using afloating roof to cover the liquid and relates particularly to Va sealfor sealing the edge of the roof to the inner walls of the tank.

Where it is desired to store relatively volatile liquids it has beenfound that less loss will occur from evaporation if floating roof tanksare used. In these tanks there is substantially no clearance between thetop of the liquid and the roof of the tank, as the roof floats on theliquidl and rises and falls with the liquid level. These tanks have amaximum volume above which the roof does not rise and have a minimumvolume wherein the roof rests on supports at the bottom of thevtank whenthe liquid level falls below the top of the supports.

In storage tanks of the floating roof type it is necessary to provide aseal between the edge of the roof and the inner surface of the tank soas to prevent losses of the stored liquid due to evaporation. The sealmust not resist the rising and falling of the roof and must provide avery tight seal, as tanks of this type are used for storing veryvolatile liquids. If evaporation were permitted to occur the loss ofliquid would be very great.

I have invented a new type seal for a floating roof tank wherein theseal does not resist when the roof rises and falls, and yet provides atight seal between the roof and the tank shell. The new seal comprises aflexible, substantially liquidimpervious member extending around thetank -from the floating roof to the inside surface of the tank and formsa trough therebetween at all positions of the roof. This trough issubstantially filled with a liquid having a specific gravitysubstantially equal to that of the liquid within the tank. With such astructure the exible member is hanging freely in a liquid, and forms atight, impervious seal.

One embodiment of the invention is set out in the accompanying drawings.Of the drawings Fig. 1 is a vertical section through the oating rooftank with the roof at its topmost position; Fig. 2 is a section similarto Fig. 1 showing the roof in an intermediate position; Fig. 3 is asection similar to Fig. 1 showing the roof still lower in the tank; Fig.4 is a section similar to Fig. 1 showing the roof in the bottom half ofthe tank; Fig. 5 is a section similar to Fig. 1 showing the roof at itslowest position in the tank; Fig. 6 is an enlarged fragmentary verticalsection of the edge of the roof; Fig. 'I is an enlarged fragmentaryvertical section showing the bottom of the 2 tank; Fig. 8 is a plan viewthis invention wherein Figs. 1 to 5 inclusive are l taken along thesection lines shown, and Fig. 9

is an elevation of the tank embodying this invention with portionsbroken away for clarity of illustration.

The floating roof tank embodying this invention comprises an outercylindrical shell I0 having a liquid II stored therein. On top of thestored liquid is located a roof I2 which floats thereon. The floatingroof includes a fiat base I3 around which is positioned a verticalchannel beam I4. On top of the flat base I3 of the floating roof arelocated sealed air chambers I5.

A fabric curtain I6 is fastened to the oating roof I2 and the shell I0of the tank so as to extend between them and form a trough I1. Thefabric curtain ls fastened to the floating roof by bolting it betweenthe channel beam Il and the flat base I 3 of the roof by bolts 24. Theother edge of the curtain is fastened to the inner surface of the shellI0 by bolting this edge to the shell and the curtain is held in place bymeans of a circular metal bar Il fastened to the tank by means of boltsI9.

The liquid-impervious curtain I6 hangs between the floating roof I2 andthe shell I0 to form a trough in all positions of the roof. In a tank43% feet high the outer edge of the curtain is fastened approximately 25feet beneath the top of the tank, and when the tank is full, as shown lnFig. 1, the trough extends substantially 2 feet beneath the line whereis is fastened to the shell. Thus, as there is a trough provided whenthe tank is full, this trough will exist at all lower positions of theroof.

between the curtain I6 and the shell III with a sealing liquid 20 havingsubstantially the same specific gravity as the liquid II Within thetank. This means that the curtain I6 hangs freely in a liquid medium andthe pressure on each side of the curtain is the same at all positions ofthe roof.

The volume of the sealing liquid 20 remains constant throughout thetravel of the floating roof and the fabric curtain changes shape asshown in Figs. 1 to 5 inclusive, as the liquid pressure on each side ofthe curtain remains constant. When the roof I2 is at its highest pointin the tank (Fig. 1) the curtain is bowed outward toward the shell. Thissame thing holds true at an intermediate position between the highestpoint of rise of the roof and a middle point (Fig. 2). When the oatingroof is down toward the of a tank embodying 3 bottom of the tank thefabric curtain bows inward (Figs. 3 to 5 inclusive). Because the curtainhas the eect of hanging freely in a liquid with pressure on both sidesof the curtain being the same, the volume enclosed by the curtain andthe shell I of the tank is the same at all positions of the roof I2.

The fabric curtain used to hold the sealing liquid 20 must beliquid-impervious, so that there can be no leakage through the curtain.A suitable curtain is made from a fabric impregnated with aliquid-impervious flexible solid material such as a synthetic rubber.One of the best materials for this purpose is neoprene.

The dimensions of the fabric curtain are not of vital importance, solong as a trough is formed at all times between the floating roof andthe shell of the container. In the embodiment shown, where the tank is100 feet in diameter. 435/2 feet tall, and the outer edge of the curtainis fastened 25 feet from the top of the-tank, the curtain will extenddown about 2 feet from the line where it is fastened to the shell.

With the dimensions given above and the edge of the floating roof beingabout 8 inches from the shell of the tank the curtain in Fig. 1 willaverage about 41/2 inches away from the shell. As shown inFig. 2, thisdistance will be about 7 inches; in Fig. 3, 12 inches; in Fig, 4, l5inches; and in Fig. 5, 24 inches. The volume of the liquid contained bythe curtain will be the same at all positions of the roof.

It is preferred that the curtain not be permitted to rub against itselfor against the shell of the tank during the roofs travel. This will nothappen where the specific gravity of the sealing liquid is substantiallyequal to the specific gravity of the liquid in the tank.

In order to assist in holding the curtain down there is preferablyprovided a weight at the bottom of the curtain, and this weight mayconsist of a bar 2l arranged in a circle of smaller diameter than thediameter of the tank and having a circular cross section. Around thisbar is located a coil spring 22 of larger diameter than the diameter ofthe rod 2l. As the roof rises and falls the coil spring rolls in thecurtain and thereby prevents the rubbing of the rod against the curtain.

In order that the curtain I6 will not be folded upon itself and presseddown by the roof when the tank is substantially empty of liquid, thereis provided a framework 23 upon which the floating roof rests when inits lowermost position (Fig.

Having described my invention together with one embodiment of the same,it is my intention that the invention be not limited by any of thedetails of description but rather be construed broadly within its spiritand scope as set out in the accompanying claims.

I claim:

1. A seal for a floating roof tank or the like comprising a flexiblesubstantially liquid-imper- Y 4 vious cylindrical curtain extendingaround the tank, said curtain having one peripheral .edge secured to thefloating root and having the other edge secured tothe side of the tankto form a trough therebetween at all positions o'f the roof, the lengthof the curtain between its edges being substantially equal to twice theminimum depth of the desired trough plus one half of the vertical travelof the roof within the tank plus the distance between the point ofattachment of the curtain to the tank and the midpoint of the rooftravel within the tank and a weight located at the bottom of the troughand freely movable relative to said curtain with vertical movement ofthe roo 2. The seal of claim 1 in which said weight comprises a liquidsubstantially filling the trough at all positions of the roof within thetank.

3. The seal of claim 2 in which said liquid has substantially the samespecific gravity as that of the liquid within the tank.

4. The seal of claim 1 in which said weight comprises an endless rod ofsubstantially circular cross section surrounded by a coil spring ofgreater diameter than the rod and normally contacting the rod only atthe bottom thereof.

5. A seal for a floating roof tank 0r the like comprising a flexiblesubstantially liquid-impervious cylindrical curtain extending around thetank, said curtain having one peripheral edge secured to the floatingroof and having the other edge secured to the side of the tank to form atrough therebetween at all positions of the roof, the length of thecurtain between its edges being substantially equal to twice the minimumdepth of the desired trough plus one half of the vertical travel of theroof within the tank plus the distance between the point of attachmentof the curtain to the tank and the midpoint of the roof travel withinthe tank, whereby said curtain forms a trough having a substantiallyconstant volume at all positions of the roof, said trough beingsubstantially filled with a liquid at all positions of the roof Withinthe tank.

6. The seal of claim 5 in which said liquid has substantially the samespecific gravity as that of the liquid within the tank.

JOHN W. ALLEN.

REFERENCES CITED The following references are of record in the illeofthis patent:

UNITED STATES PATENTS Number Name Date 2,050,686 Wiggins Aug. 11, 19362,297,985 Rivers Oct. 6, 1942 2,307,508 Jayne Jan. 5, 1943 2,408,538Wiggins Oct. 1, 1946 FOREIGN PATENTS Number Country Date 106,097Australia Dec. '1, 1938

